MATEC Web of Conferences 4, 04003 (2013)
DOI:
10.1051/matecconf/20130404003
C Owned by the authors, published by EDP Sciences, 2013
Physico-chemical and membrane-interacting properties of D-xylose-based
bolaforms. Influence of the anomeric configuration
M. N. Nasir1, V. Legrand1, S. Gatard2, S. Bouquillon 2, K. Nott1, L. Lins3 and M. Deleu1 *
1
Unité de Chimie Biologique Industrielle, Université de Liège, Gembloux Agro-Bio Tech, Passage des déportés,2, B-5030
Gembloux, Belgium.
2
Université de Reims Champagne-Ardenne, Institut de Chimie moléculaire de Reims UMR CNRS 6229, boîte no 44, B.P.
1039, 51687 Reims, France.
3
Centre de Biophysique Moléculaire Numérique, Université de Liège, Gembloux Agro-Bio Tech, Passage des déportés,2,
B-5030 Gembloux, Belgium.
*Corresponding author: magali.deleu@ulg.ac.be
Abstract. Sugar-based biosurfactants such as xylose-derived bolaforms have interesting properties, for
example high biocompatibility and biodegradability which make them potential useful molecules in the
pharmaceutical and cosmetic fields. Until now, no detailed analyses of the physico-chemical properties of these
compounds have been undertaken. Two symmetrical D-xylose-based bolaforms were chemically synthesized
where the two xylose heads are linked via an acetal link to a hydrocarbon chain containing 18 carbon atoms
and an unsaturation. The two bolaforms differ only by their anomeric configuration: or The
bolaform exhibits interfacial properties at the air-water interface which is not the case for the . FTIR
spectroscopy showed that the interactions between the bolaform and POPC, a model phospholipid, involve
the carbonyl groups of the phospholipid.
1 Introduction
During recent years, sugar-based biosurfactants
have attracted increasing interest because of their high
biocompatibility and biodegradability [1]. Our work has
focused on xylose-based bolaforms, a particular class of
sugar-based biosurfactants. They are symmetric
molecules composed of two polar heads, each consisting
by a xylose unit, connected by a hydrophobic carbon
chain.
This work studies the influence of the anomeric
carbon configuration on the physico-chemical properties
of xylose-based bolaforms. For that purpose, two
symmetrical bolaforms (XC18  unsat and XC18 
unsat) were chemically synthesized in two steps. In the
first, the D-xylose is connected by an acetal link to a
hydrocarbon carbon chain containing 10 carbon atoms
and a terminal unsaturation. In the second step, two
subunits are linked together by metathesis. These two
molecules differ only by the configuration of the
anomeric carbons which are either  or  (Figure 1).
Figure 1: Simplified scheme of the two step-chemical synthesis
of the two bolaforms from D-xylose (n = 5). XC18  unsat =
1-18-bis-octadéc-9-ényl-α-D-xylopyranoside; XC18  unsat =
1-18-bis-octadéc-9-ényl--D-xylopyranoside.
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Article available at http://www.matec-conferences.org or http://dx.doi.org/10.1051/matecconf/20130404003
MATEC Web of Conferences
The interfacial properties of these two molecules were
initially studied by tensiometry and their critical
aggregation concentration (CAC) was determined when
pertinent. Then the interactions of XC18  unsat with a
model phospholipid, 1-palmitoyl-2-oleoyl-sn-glycero-3phosphocholine (POPC), were analyzed in a biomimetic
membrane system using FTIR spectroscopy.
2 Materials and Methods
2.1 Chemical Syntheses
The chemical synthesis of the D-xylose based
bolaforms used in this work has been previously reported
[1]. The purity of each compound was checked by RPHPLC-ELSD and was found superior to 97%.
2.2 Tensiometry measurements
Surface tension was measured with a Tensimat N3
tensiometer equipped with a platinum Wilhelmy plate.
All measurements were performed at 25°C. The
bolaforms were dissolved in DMSO and injected into the
subphase (ultrapure water) so as to reach different final
concentrations ranging from 0.625 to 20 µM as described
in [1,2].
2.3 Preparation of multilamellar vesicles (MLV)
samples
Multilamellar vesicles containing POPC or POPC
with bolaform were prepared as described in [3].
Figure 2: Adsorption experiments of XC18  unsat and
XC18  unsat at the air-water interface monitored by the
increase of surface pressure as a function of time. The final
concentration of each bolaform in the subphase was 2.5 µM.
After the injection of the bolaform , the surface
pressure increased before reaching a plateau while no
increase of surface pressure was detected with the
bolaform even at higher concentration. The
modification of the anomeric configuration from 
to for these bolaforms led to a complete loss of
surfactant properties. Aggregates were observed in the
bulk phase suggesting an insolubilization phenomenon
when the anomeric form is  We then focused only on
the bolaform . In order to characterize the aggregation
behavior of the bolaform , we injected the molecule at
different concentrations and followed the evolution of
surface pressure. Figure 3 gives the variation of the
equilibrium surface pressure as a function of the
concentration in the subphase.
2.4 FTIR Spectroscopy
Infrared spectra were recorded by the means of the
Bruker Equinox 55 spectrophotometer after 128 scans at
4 cm-1 resolution. The spectrophotometer was purged
with dry air in order to remove any undesired water
vapor. All experiments were performed with a
demountable cell equipped with CaF2 windows as
described in [3]. The spectrum of 2H2O alone was
subtracted from the sample spectrum taken under the
same conditions. In the case of MLV spectra, a 20 μL
sample of the different MLV was deposited on the CaF2
window as described in [3].
3 Results
Figure 3 : Maximal surface pressure variation as a function of
the concentration of the XC18  unsat injected into an
ultrapure water subphase.
3.1 Characterization of interfacial properties
We investigated the interfacial properties of XC18
 unsat and XC18  unsat by adsorption experiments
at the air-water interface. For each bolaform, Figure 2
gives the evolution of surface pressure as a function of
the time after their injection at 2.5 µM into the subphase
(ultrapure water).
The variation of surface pressure increased with
increasing concentrations of bolaform  and reached a
plateau above 5 µM. From this curve, the critical
aggregation concentration of the bolaform  and the
corresponding surface tension, CAC, was determined to be
4.4±0.8 µM and 54 mN/m, respectively. In comparison to
other conventional surfactants [4-6] this CAC value is
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ICOMF14
very low. This suggests the high capacity of the bolaform
 to aggregate.
3.2 Interaction of the bolaform  with POPC
MLVs
Previous studies reported that XC18  unsat was
able to penetrate and interact with Langmuir monolayers
and bilayers of phospholipids [1,2]. In order to gain more
information at the molecular level, we analyzed the
interactions of the bolaform  with POPC in MLVs
using infrared spectroscopy. Figure 4a and 4b gives the
1850-1650 cm-1 and 1100-900 cm-1 regions of the
infrared spectra of POPC MLVs in the presence or in the
absence of XC18  unsat, respectively.
900cm-1 region, the spectrum of pure POPC MLVs shows
three major bands located at 1088, 1063 and 970 cm-1.
The band at 1088 cm-1 could be attributed to the
symmetric stretching vibrations of PO2- groups of POPC,
the band at 1063 cm-1 to the symmetric stretching
vibrations of C-O-C bound and the band at 970 cm-1 to
the asymmetric stretching vibrations of choline groups
[8]. When bolaform  was inserted into POPC MLVs,
the band at 1063 cm-1 was shifted to 1052 cm-1. This
suggests that the interactions of the bolaform with POPC
MLVs involve the C-O-C groups of the lipid. No change
is observed for the bands at 1080 cm-1 and 970 cm-1
suggesting that the choline groups of POPC are not
involved in these interactions.
4 Conclusions
This work was carried out on a novel series of
bolaforms having two D-xylose heads connected to each
other with an hydrocarbon chain and differing only by
their anomeric carbons which were  or . The
interfacial behavior of these two bolaforms was
investigated by tensiometry measurements. The bolaform
 was found to have interfacial properties while the
bolaform  shown none whatsoever, it was located in
the bulk phase. This could be due to the difference of
conformation adopted by these two molecules which
could favor an aggregation when the anomeric form is
. The interactions of the bolaform  with a model
phospholipid, POPC, were investigated at the molecular
level by infrared spectroscopy. Our results showed that
these interactions involve the C=O of the ester groups
and the C-O-C bonds of the phospholipid. More detailed
analyses of this interaction involving the acyl chains of
the phospholipid will be performed using a deuterated
phospholipid in order to discriminate them from the
bolaform hydrophobic chain. This work offers a non-food
valorizations of pentoses (xyloses) extracted from
lignocellulosic biomass as surfactants, therapeutic or
cosmetic agents for encapsulation.
0.5
Absorbance
0.4
0.3
0.2
0.1
0
1850
POPC
POPC + XC18  unsat
1800
1750
1700
-1
Wavenumber (cm )
0.2
1650
POPC
POPC + XC18  unsat
Absorbance
0.15
0.1
0.05
Acknowledgements
0
1100
1050
1000
950
-1
Wavenumber (cm )
900
Figure 4: FTIR spectra of the POPC MLVs with or without
bolaform XC18 unsat. Two regions of the spectra were
presented.
In the 1850-1650 cm-1 region, the spectrum of pure
POPC MLVs shows a band centered at 1740 cm-1 with a
shoulder at 1725 cm-1 which could be attributed to the
C=O groups of POPC [7-8]. The band at 1740 cm-1
corresponds to the free C=O groups while the shoulder at
1725 cm-1 corresponds to the hydrogen-bounded C=O
ester groups. When the bolaform was inserted into POPC
MLVs, the shoulder became less important and shifted
slightly to low wavenumber. Even though this change is
small, it could suggest an interaction between POPC and
bolaform involving C=O ester groups. In the 1100-
M.N.N thanks the University of Liege for his
postdoctoral position. M.D. and L.L. thanks the Belgian
National Foundation for Scientific Research (FNRS) for
their positions as Research Associate and Senior
Research Associate, respectively. K. N. thanks the
Superzym ARC grant, financed by the French
Community of Belgium.
The authors thank the Walloon Region (through the
Excellence Program « TECHNOSE ») for the financial
support.
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